Various methods have previously been known for the production of microspherical cured phenolic resin particles. For example, U.S. Pat. Nos. 3,823,103, 4,026,828, 4,039,525 and 4,316,827 disclose methods for producing microspherical cured phenolic resin particles by subjecting phenols and aldehydes to emulsion polymerization in aqueous media in the presence of protective colloids such as gum arabic, gum ghatti, hydroxyalkylated guar gum or partially hydrolyzed polyvinyl alcohol, and a basic catalyst. According to these methods, microspherical phenolic resin particles having thermal reactivity are formed as solid particles of a so-called resol resin, and then under a selected set of reaction conditions, converted into microspherical cured resol resin particles.
Japanese Patent Publication No. 42077/78 discloses that not only microspherical resol resin particles having thermal reactivity but also microspherical cured resol resin particles can be produced by reacting a phenol with formaldehyde using a basic catalyst in the presence of a nitrogen-containing compound such as ethylenediamine, adding a hydrophilic organic polymer such as gelatin, casein, or polyvinyl alcohol to the resulting condensate, and continuing the reaction further. This patent document shows that the microspherical cured resol resin particles can be used as a lightweight filler for resins in the fields of molding materials, laminated articles, adhesives, etc.
U.S. Pat. No. 4,414,379 discloses a method for producing microspherical cured phenolic resin particles or microspherical phenolic resin particles having thermal reactivity by reacting a phenol with a large excess (8 to 10 mols per mol of the phenol) of formaldehyde in an aqueous medium using hydrochloric acid as a catalyst. Since this method is based on the reaction of the phenol and a large excess of formaldehyde, it differs from the aforesaid methods of producing microspherical cured resol resins. Table 9 of U.S. Pat. No. 4,414,379 shows the fluxural strengths of carbonized products obtained by mixing the microspherical cured phenolic resin particles obtained by the method of said patent and the aforesaid microspherical cured resol resin particles with a phenolic resin having thermal reactivity, molding the mixture, and subjecting the molded articles to a carbonizing treatment. When the microspherical cured resol resin particles are mixed, the resulting carbonized product has a very low flexural strength, and cannot be used for practical purposes. The fexural strength of the carbonized product obtained in the case of mixing the microspherical cured phenolic resin particles is not high and does not prove to be very satisfactory. Furthermore, the microspherical cured phenolic resin particles obtained by this method have the defect that their particle size distribution is broad and most of the resin particles become secondary agglomerated particles. In addition, this process is economically disadvantageous since formaldehyde is used therein in a large excess amount.